Radar system for obstacle warning and imaging of the surface of the earth

ABSTRACT

A radar system for active obstacle warning and imaging of the surface of the earth, working in the pulse frequency or FH-CW range, which can be used in on-line operation in real time, includes a plurality of antenna elements for sending and receiving radar signals, which are arranged on the fuselage of an aircraft, and which may be turned on and scanned sequentially, whereby a synthetic aperture can be generated by means of periodic sending and receiving of the antenna elements. Antenna elements are arranged along the curved surface of the aircraft contour, whereby a SAR processor is present, which analyzes the data obtained from the antenna elements and displays them as processed radar images on board the aircraft, in a virtual cockpit.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of GERMAN Application No.10120536.8 filed Apr. 26, 2001. Applicants also claim priority under 35U.S.C. §365 of PCT/DE02/01496 filed on Apr. 24, 2002. The internationalapplication under PCT article 21(2) was not published in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a radar system for obstacle warning and imagingthe surface of the earth.

2. The Prior Art

A radar system for obstacle warning and imaging the surface of the earthis known from DE 40 07 612 C1. There, a forward-view radar is described,which is attached to the fuselage of an aircraft, and images the sectorregion lying ahead of the aircraft in two dimensions. In thisconnection, the forward-view radar described comprises an antennaconsisting of several antenna elements arranged next to one another, forsending and receiving. By means of turning on and scanning the antennaelements, in a time sequence, one after the other, a synthetic apertureis generated, as it is known from the SAR principle. In this connection,the analysis of the radar signals takes place in such a manner that eachantenna element is analyzed individually, whereby digital processing iscarried out for each angle range, by means of correlation of a special,predetermined referenced function. A disadvantage in this connection isthe poor angle resolution. Other analysis methods are known from Fan, Z.F. et al., in “High Resolution Imaging of Objects at Ka Band,” IEEETrans. on Aerospace and Electronic Systems, 1995, Vol. 31, Issue 4, p.1348–1352, and Li, H.-J. et al., in “Nonuniformly Spaced Array Imaging,”IEEE Trans. on Antennas and Propagation, 1993, Vol. 41, Issue 3, page278–286.

The radar system known from DE 40 07 612 C1 proves to be disadvantageousin that it can only image the forward-lying sector region. Regionsadjacent to the side must be imaged by means of additionally installedantenna systems. This means a significant installation effort andexpenditure. In addition, complicated analysis methods are required inorder to be able to image the various sector regions.

SUMMARY OF THE INVENTION

It is therefore the underlying object of the invention to indicate asingle radar system with which not only a forward view but also a sideview is possible.

This object is accomplished using the radar system according to theinvention. Advantageous embodiments of the invention are also described.

According to the invention, the antenna elements are arranged along thecurved surface of the aircraft contour, whereby an SAR processor ispresent, which analyzes the data obtained by the antenna elements anddisplays them as processed radar images on board the aircraft, in avirtual cockpit.

The antenna elements can now be advantageously turned on in accordancewith the sector region to be imaged. The data obtained from the antennaelements, in each instance, can be advantageously analyzed according tothe linear SAR method or according to the ROSAR method.

In the proposed radar system, the synthetic aperture known from theconventional SAR method is not generated in that the aircraft movesrelative to the target object, for example, but rather the individualantenna elements, arranged adjacent to one another, are electronicallyturned on and scanned, in a time sequence, one after the other. In theanalysis according to the ROSAR method, as well, the rotating antennamovement is simulated by means of turning on and scanning adjacentantenna elements, with a time offset.

In an advantageous embodiment of the invention, the antenna elements arearranged spatially in order to generate a three-dimensional radarsystem. In this connection, the antenna elements are brought together astwo-dimensional antenna arrays, which are adapted to the curved contourof the aircraft and affixed on the aircraft.

An advantage of this spatial arrangement of the two-dimensional antennaarray on the contour of the aircraft is that the scanning plane of theantenna elements is uncoupled from the flight plane of the aircraft.This means that the scanning plane can be kept constant, independent ofthe flight plane. In the case of severe air turbulence or when theaircraft is flying and turning, in particular, it can happen that theobject to be imaged disappears from the viewing range of the radar. Thisis prevented by the two-dimensional antenna array advantageouslyarranged along the contour of the aircraft.

The radar system according to the invention can advantageously be usedalso on fighter and/or reconnaissance drones or ships. In thisconnection, it can be used as an all-weather viewing system, in eachinstance, and allows aircraft, for example, to land and take off safelyeven on airports that are not specifically equipped, in any weather.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention as well as other advantageous embodiments will beexplained in greater detail in the following, using drawings. Theseshow:

FIG. 1 an exemplary embodiment for the installation of the antennaelements into the region of a radar nose of an aircraft, in a schematicrepresentation;

FIG. 2 an exemplary embodiment of an electrical block schematicaccording to FIG. 1;

FIG. 3 a diagram with reference to the sequence of sending and receivingsignals according to the exemplary embodiment according to FIG. 1;

FIG. 4 exemplary embodiments of the arrangement of antenna elements inradar noses of various shapes;

FIG. 5 a schematic diagram with reference to an exemplary embodiment foran antenna arrangement according to the ROSAR principle and the linearSAR principle;

FIG. 6 an exemplary embodiment of a surface arrangement of the antennaelements in the region of a radar nose of an aircraft, in a schematicrepresentation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a schematic representation of a first exemplary embodimentof the arrangement of the antenna elements along the contour of theaircraft. Sending and receiving antenna elements A are mounted on acurve that corresponds to the contour K of the aircraft, for example, ata distance Δb, in the region of the radar nose RN. In this connection,Δb is λ/2, whereby λ is the wavelength of the sending signal.

FIG. 4 shows two other exemplary arrangements of the antenna elements,whereby the view of an aircraft from below is shown as an example, ineach instance. Of course this arrangement can also be transferred to thetop view or side view of the aircraft. In the arrangement on the left,the antenna elements A are arranged along the contour of the aircraft,towards the tip of the radar nose RN of the aircraft. In thisconnection, the arrangement of the antenna elements A along the contourof the aircraft can occur as any desired curve.

The representation on the right in FIG. 4 shows another exemplaryarrangement possibility of the antenna elements A along the contour ofthe aircraft. For reasons of the representation, the arrangement of theantenna elements A appears as a circle in this connection, although inreality, the antenna elements A are arranged along a curve that isadapted to the contour of the aircraft.

FIG. 2 shows a block schematic of the electrical wiring of an exemplaryembodiment according to FIG. 1. During a time Δt, the sending andreceiving antennas A are switched to a phase-stable HF transmitter S, ineach instance, and afterwards, during the time Δt, to a receiver E. Thecontinuous, rotatory movement of the antennas that occurs in connectionwith the ROSAR principle, for example, is carried out electronicallyhere, by switching the HF transmitter S on from one antenna element A tothe next. In this connection, a reflex point on the runway that is to beimaged (not shown) or a point (not shown) in its vicinity is given asending signal that is changed in phase over time. In the receivingphase, the receiver E also receives a signal that is changed in phase. Apositive Doppler shift that changes over time occurs, as long as theantenna scanning moves towards the reflex point.

As soon as the antenna scanning moves away from the reflex point, anegative Doppler shift that changes over time is generated. The overlayof the Doppler history, i.e. the phase history over the original sendingsignal at a constant frequency is calculated for every lateral positionof a reflex point, such as, for example, in the ROSAR standard methodfor helicopters, but with inclusion of the flight velocity.

As in the standard method, the reflection of a reflection point that isan image point of the scene to be imaged is determined using across-correlation, performed in a correlator K, of the received signalmixture with the reference signal of this reflection point, which isderived from the reference signal memory RS. Here again, in the presentcase the individual reference signals, with the exception of specialcases, differ for a distance ring only by the angle position, so that aseparate reference signal does not have to be stored in memory andcorrelated for every reflection point.

In contrast to the ROSAR radar system, in which the helicopter isassumed to be at rest, the problem of a rapid change in distance due tothe high flight velocity occurs with the radar system proposed here, andthis results in image distortion. Aside from the possibility of modelingthe entire movement sequence and thereby being able to include it in allthe calculations, particularly in the image distortion correction, theelectrical scanning offers an extreme shortening of the entire scanningcycle, so that the effect of the change in distance results in an imagedistortion that is small enough to be ignored. In this way,calculation-intensive image distortion correction is not necessary.

FIG. 3 shows an exemplary embodiment for the progression of sending andreceiving signals with their “sending” and “receiving” intervals. Theprogression of adjacent antenna elements being turned on, which repeatsover time, is shown on the abscissa. The first antenna element sends theshort transmission pulse S1 during the time Δt_(s). During thesubsequent time span Δt_(e), the first antenna element receives thesending signal E1. The amplitude of the sending and receiving signal isshown on the ordinate, without any units.

Furthermore, it is proposed that pilot visual equipment is present, inwhich the radar data that are obtained can be displayed. For example, avirtual cockpit can be present, in which a three-dimensional computerimage of the surroundings is imaged, for example.

By means of displaying a current image of obstacles in the virtualcockpit, a significant increase in the efficiency of computer-orientedflight control can be achieved. The virtual cockpit requires currentlocation data from GPS. Because of the required position accuracy, themore suitable “differential GPS” is proposed for this purpose. If thereis any need to efficiently transmit position or obstacle data, either anHF/VHF data link or mobile communications via GSM or satellite networkare proposed. The use of mobile communications allows two-waycommunications, i.e. full duplex operation and group communication. Theadvantage of HF/VHF communication lies in the independence fromavailable infrastructures. Autarchic communication possibilities areparticularly required for military deployments in partly unknownterritory.

FIG. 5 shows another exemplary embodiment of the radar system accordingto the invention. In this connection, a cross-section through thefuselage of an aircraft is shown. It is advantageous if the radar dataof the antenna elements of the segment KA of the antenna array on thefuselage, which is shown as a circle, as an example, are analyzedaccording to the ROSAR method. It is advantageous if the segment LA ofthe antenna array, which follows this segment KA, is analyzed accordingto the linear SAR method.

By means of this advantageous combination of the two analysis methods,the radar system according to the invention makes an all-around viewpossible, without a “squint mode” being required, for example, whichwould be connected with losses in resolution, i.e. an increased signalprocessing effort because of the slanted antenna sight angle.

FIG. 6 shows another exemplary embodiment of the radar system accordingto the invention. In this connection, a schematic representation of theradar nose RN of an aircraft is shown in a side view. The antennaelements A are arranged on the surface, in accordance with the contour Kof the aircraft. In this connection, the antenna elements A are broughttogether in antenna arrays, which are not shown in the drawing, for thesake of a better overview.

In this connection, the arrangement of antenna elements A shown ismerely exemplary. Of course a different arrangement of the antennaelements A is also possible.

1. Radar system for active obstacle warning and imaging of the surfaceof the earth, working in the pulse frequency or FM-CW range, which canbe used in on-line operation in real time, comprising a plurality ofantenna elements for sending and receiving radar signals, which arearranged on the fuselage of an aircraft, and which may be turned on andscanned sequentially, whereby a synthetic aperture can be generated bymeans of periodic sending and receiving of the antenna elements, whereinthe antenna elements are arranged along the curved surface of theaircraft contour, whereby a SAR processor is present, which analyzes thedata obtained from the antenna elements and displays them as processedradar images on board the aircraft, in a virtual cockpit; and whereinthe synthetic aperture that is generated from a first predeterminedsegment of the antenna elements is processed according to the linearROSAR method; and wherein the synthetic aperture that is generated froma second predetermined segment of the antenna elements is processedaccording to the linear SAR method.
 2. Radar system according to claim1, wherein the time for a scanning cycle is selected in such a mannerthat despite the airplane movement, no distortion of the image of theoutdoor scene to be imaged occurs, which is also referred to as smudgingof image points.
 3. Radar system according to claim 1, wherein thecalculation of reference signals for important image points of theoutdoor scene takes place according to the known ROSAR method, but withadditional consideration of the flight velocity.
 4. Radar systemaccording to claim 1, wherein in order to form a three-dimensional radarsystem, the antenna elements, brought together in antenna arrays, arepositioned appropriately in terms of space.
 5. Radar system according toclaim 1, wherein the data obtained can be displayed as athree-dimensional computer image in the virtual cockpit.
 6. Radar systemaccording to claim 1, wherein in order to increase the efficiency ofcomputer-oriented flight control, the current obstacles can be displayedin the virtual cockpit.
 7. Radar system according to claim 1, whereinthe current position data can be input into the virtual cockpit by meansof GPS or differential GPS.
 8. Radar system according to claim 1,wherein an HF/VHF data link is present, with which an efficienttransmission of the position and obstacle data by means of mobilecommunications via GSM or satellite network is possible.
 9. Radar systemaccording to claim 1, for use in battle and/or reconnaissance drones.